1. Field of the Invention
The present invention relates to an illuminating apparatus, a pattern inspection apparatus, and a method of forming illuminating light, and for example, relates to an illuminating apparatus that reduces coherence of coherent light, a pattern inspection apparatus that inspects an object to be a target object used for fabricating a semiconductor for pattern defects by using illuminating light of such an apparatus, and a method of forming the illuminating light.
2. Related Art
In recent years, with increasingly higher integration and larger capacity of LSIs, the line width of a circuit demanded for semiconductor devices is becoming increasingly narrower. Such semiconductor devices are fabricated by exposing and transferring a pattern onto a wafer using a reduced projection aligner, a so-called stepper, to form a circuit using an original pattern (also called a mask or reticle) on which a circuit pattern is formed. Thus, for the fabrication of a mask to transfer such a fine circuit pattern onto a wafer, a pattern writing apparatus capable of writing a fine circuit pattern is used. By using such a pattern writing apparatus, a pattern circuit may directly be written onto the wafer. For example, an electron beam or laser beam is used to write a pattern.
In addition, improving yields is indispensable for fabrication of LSIs requiring huge fabrication costs. However, patterns forming an LSI are moving, as is typically observed in a DRAM (random access memory) of 1 gigabit or so, from a submicron to the order of nanometer. As a major factor that reduces yields, pattern defects of a mask used when a hyperfine pattern is exposed and transferred onto a semiconductor wafer by photolithography technology can be cited. In recent years, with increasingly finer LSI dimensions of patterns formed on a semiconductor wafer, dimensions that need to be detected as a pattern defect have become extremely small. Thus, a pattern inspection apparatus that inspects a transfer mask used for LSI fabrication for defects needs to be more precise.
On the other hand, with the development of multimedia, liquid crystal displays (LCDs) have an increasingly larger liquid crystal substrate size of 500 mm×600 mm or more and finer patterns such as thin film transistor (TFT) formed on the liquid crystal substrate. Thus, inspection for extremely small pattern defects in a wide range is increasingly required. Therefore, development of a pattern inspection apparatus that inspects a photomask used for fabricating such a large-area LCD pattern and a large-area LCD for defects efficiently in a short time is also urgently needed.
With increasingly finer mask patterns and higher integration, higher resolution is required from an inspection apparatus and the wavelength of illuminating light of the inspection apparatus becomes shorter. For example, deep ultraviolet light with a wavelength of 266 nm or less is used. Such illuminating light is oscillated from a laser light source apparatus. However, laser light emitted from such a laser light source is a coherent light, causing a problem in that certain interference fringes (speckles) arise due to coherence. Thus, attempts are made to eliminate coherence by, for example, passing a light beam from a light source through a fly's eye lens and further passing the passed light beam through a rotating phase plate (see, for example, Japanese Patent Application Laid-Open No. 11-72905).
As described above, attempts to eliminate coherence of coherent light have been made, but no technique to adequately solve the problem has been established.